Electromagnetic energy adaptation material

ABSTRACT

The invention discloses an electromagnetic energy adaptation material, which can absorb electromagnetic energy, the material including a mixture of at least one liquid with at least one surfactant. The liquid may be a dipolar molecular liquid, and may be pressurized by means of a gas. Further the use of an electromagnetic energy adaptation material in the form of a foam for covering an object to prevent detection thereof by an electromagnetic energy detection apparatus, such as radar equipment, is disclosed. Finally a method of minimizing or altering detection of an object by means of electromagnetic energy detection apparatus is suggested, which includes the steps of coating such an object or a zone spaced away from such an object at least partially by means of a foam of an electromagnetic energy adaptation material.

FIELD OF INVENTION

The present invention relates to electromagnetic energy adaptationmaterial.

More particularly, the invention relates to electromagnetic energyadaptation material, which is capable of absorbing or altering thereflection or emission of electromagnetic energy thereby enabling a bodycovered by the material to appear to be different than what it truly is.

BACKGROUND TO INVENTION

An electromagnetic wave absorber is a material that is designed toexhibit a balance between wave reflection, wave transmission and waveabsorption or otherwise influence an electromagnetic wave incident uponit. The interaction between an electromagnetic wave and a medium isdescribed completely by the complex permittivity and permeability. Inthe case of a non-magnetic medium, the complex permittivity describesthe material completely, and thus the reflection, transmission andabsorption coefficients. An efficient or effective electromagnetic waveabsorber is one that minimises surface reflection and at the same timehas sufficient absorptive properties so that transmitted radiation isreduced. The main object is to replace the appearance of an object by asmaller or different one determined by a cloaking material designed tohide the object.

In designing an electromagnetic wave absorber, one attempts to employsubstances, which offer control of the loss mechanism and by way ofthis, offer control of the parameters governing the magnitude of theincident reflection. Sometimes other physical properties may play a rolein the ability to influence the absorption or alteration ofelectromagnetic radiation. The thermal conductivity and emisivity aretwo parameters that can be exploited to further alter the appearance ofa covered body.

In the present state of the art, control of microwave reflectivity hasbeen demonstrated by simultaneous control of the bulk density of thematerial and the volume concentration of additives used to introduce theloss. The substances employed to introduce loss within the scope of thepresent state of the art are typically substances that exhibit Ohmiclosses. At a sufficient volume fraction of this additive, a controlledinterparticle contact between the Ohmic particles is achieved whichproduces macroscopic conductivity throughout the bulk of the medium. Aproper balance between the macroscopic conductivity and density producematerials which can exhibit excellent absorptive properties over a wideband, typically between 2 to 18 GHz. This is but a rather narrow part ofthe entire microwave frequency band. The effective bandwidth is a resultof employing an Ohmic loss mechanism in that Ohmic losses produce ahyperbolic frequency dependent loss factor. Thus, at low frequencies,the losses are so great that a degredation in surface reflectionproperties are produced while at high frequencies, the loss is so smallthat the material is not absorptive enough to prohibit high transmissionand subsequent rereflection of an incident electromagnetic wave.

Typically, carbon powder or foamed forms of carbon or resistive sheetshave been used and structures built from them produce excellentabsorptive properties between 1 to 20 GHz in the microwave frequencyband. In general, an electrically homogeneous material exhibiting aspecific level of Ohmic conductivity can only produce good reflectionloss over a narrow frequency band. Combinations of materials havingdifferent impedances may be used to covet wide parts of this band.Extremely thick shaped profiles are also used to produce broad-bandedbehaviour, especially at MHz frequencies.

Nature, however, offers another type of loss mechanism, dielectricrelaxation. Dielectric relaxation is not an Ohmic process and is basedon the fact that small molecules having a dipole moment totate in thepresence of a modulating electromagnetic field. Theoretically, theprocess is described by the “Debye relaxation process”. The most commonexample of the use of dielectric relaxation in the absorption ofmicrowaves is microwave drying and heating microwave heating and cookingis done in almost every household world wide. The size of the moleculeand its dipole moment govern where maximum interaction with the fieldwill occur and thus the frequency span of absorption of microwave energyand its transformation into thermal heating. Various physicallimitations are associated with the exhibition of dielectric losses inmaterials.

Firstly, for rotation to occur, the molecules must be free to do so.This limits the material to liquids or gasses. The size of the moleculeis associated with this in that size (inertial effects) requires thatthe molecule has a low inertia enabling it to rotate in phase to someextent with the electromagnetic radiation. Such small molecules aretypically gasses and liquids as based on their melting or boiling point.Gasses ate typically too dilute to be of any use as a microwave absorberand are in any case hard to confine. Liquids, even though they are acondensed phase are typically too dense to be used as a microwaveabsorber. Most substances do exhibit some degree of dielectrictelaxation, however, the absorption may not be as efficient as others.

Although the effect one is trying to achieve in microwave absorption issimilar to that used in microwave heating or cooking, it should berealised that although many substances such as food stuffs absorbmicrowave energy, no food stuff or any natural substance in itself isdesigned by man to absorb microwave energy efficiently or maximally.

It has been known for quite some time that water, disposed in the formof an aerosol or fine droplets can attenuate microwave tadiation withoutproducing a high initial reflection as water would in its dense state.Rain most certainly is not a stable structure as it is susceptible togravity and wind, its density cannot be controlled widely and otherwisehas to be continually generated.

It is an object of this invention to provide a novel type ofelectromagnetic energy adaptation material.

SUMMARY OF THE INVENTION

According to the invention, an electromagnetic energy adaptationmaterial, which can absorb electromagnetic energy, includes a mixture ofat least one liquid with at least one surfactant.

The liquid may be a dipolar molecular liquid.

The dipolar molecular liquid may be water.

The dipolar molecular liquid may be a glycol.

The mixture may have been pressurised by means of a gas.

The mixture may have been foamed by mechanical means.

The gas may be an emulsifiable gas.

At least one surfactant may be ionic.

At least some surfactants may be ionic and non-ionic.

At least one surfactant may be non-ionic.

The mixture may include a base agent neutralising the ionic surfactantsat least partially.

The mixture may include a soluble polymer.

The mixture may include in situ cross-linkable monomers of any molecularweight.

The mixture may include soluble dyes.

The mixture may include water dispersible dyes.

The mixture may include water dispersible pigments.

The mixture may include viscosity modifiers.

The emulsifiable gas may include short chained alkanes.

The alkane may be butane.

The alkane may be propane.

The mixture may include at least one humectant.

The material may be a foam.

The material may be a gel.

The material may be adapted to alter the reflection or emission ofelectromagnetic energy.

Further according to the invention there is provided use of anelectromagnetic energy adaptation material as set out herein in the formof a foam for covering an object to prevent detection thereof by anelectromagnetic energy detection apparatus, such as radar equipment.

The electromagnetic energy adaptation material may be in the form of afoam for covering an object to prevent detection thereof by thermaldetection equipment.

The electromagnetic energy adaptation material may be used in the formof a foam for covering an object to prevent detection thereof by laserdetection equipment.

Also according to the invention, a method of minimising or alteringdetection of an object by means of electromagnetic energy detectionapparatus, includes the steps of coating such an object at leastpartially by means of a foam of an electromagnetic energy adaptationmaterial as set out herein.

Further according to the invention, a method of minimising or alteringdetection of an object by means of electromagnetic energy detectionapparatus, includes the steps of coating a zone spaced away from such anobject at least partially by means of a foam of an electromagneticenergy adaptation material as set out herein.

The method may be applied to camouflage objects for military purposes.

Water is the small dipolar molecule which exhibits loss based on thedielectric relaxation mechanism. Other small dipolar molecules in theclass of glycols may be included or even replace water in the generalformulation. A foaming agent is defined as the material causing themedium to expand after release from a pressurised container allows thefoaming agent to undergo a phase transformation from an emulsifiableliquid into a gas. Suitable foaming agents are typified by butane andpropane or mixtures thereof. The surfactant stabilises the liquid/gasmixture so that gravity and surface tension forces are minimisedenabling the foam to retain its structure for prolonged periods of timewithout collapse.

Humectants (e.g. polyhydric alcohols, mannitol, sorbitol, glycerol andxylitol) also serve to prolong the lifetime of a water based foam inthat they reduce evaporation. The structure of the foam consists of acontinuous liquid phase termed the ‘foam concentrate’ and adiscontinuous gas phase called the ‘gas phase’.

foam's origin is also part and parcel of the ultimate function andpurpose of the foam itself. For example, if the foam employs propane asthe foaming agent then the mixture of liquified propane and foamconcentrate is the parent of the foam, i.e., it's precursor. Thus, theparent material may only exist by way of its container, as allanticipated end use scenarios would apply to atmospheric pressureconditions.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described by way of example with reference tothe accompanying schematic drawings.

In the drawings there is shown in:

FIG. 1: composite data as shown in Hasted, “Aqueous Dielectrics”, page57, FIG. 2.8, Chapman and Hall, 1973 in which frequency variation ofε′(single line and open circles) and ε″ (double line and open circles)for liquid H₂O at 25° C., broken double line represents the contributionof the principal relaxation time to ε″, and dotted lines (open dots forε″, closed for ε′) represent a first attempt to fit the secondrelaxation process;

FIG. 2: permittivity of a foam;

FIG. 3: the permittivity of the same foam as in FIG. 2 but admixed witha water soluble ink solution, wherein the solid line represents thepermittivity actually measured and the dash line represents an averageover the measured frequency;

FIG. 4: the permittivity of the same solution as in FIG. 2 but admixedwith methanol, wherein the solid line represents permittivity actuallymeasured and the dash line represents an average over the measuredfrequency;

FIGS. 5-11: permittivity of various samples in accordance with theinvention;

FIG. 12: reflectivity loss of a metal plate covered with foam asreferred to in FIG. 2;

FIG. 13: reflectivity loss of a metal plate covered with air blown foam;

FIG. 14: 94 GHz reflectivity loss of a corner reflector treated withfoam;

FIG. 15: 94 GHz reflectivity loss of a metal plate treated with foam;and

FIG. 16: UV-Visible-near infrared reflectivity of foam dyed with carbonblack.

DETAILED DESCRIPTION OF DRAWINGS

Water is an excellent choice for the small dipolar molecule exhibitingdielectric relaxation although it is not the only choice. Water'sdielectric properties have been fully characterised. In its liquid form,and water is known to be a good reflector of microwave energy.

The composite data in FIG. 1 (Page 57, FIG. 2.8, Hasted, “AqueousDielectrics”, Chapman and Hall, 1973) indicates that water would be agood reflector of microwave energy up to frequencies of 1000 GHz. Thesymbols used indicate the following:

-   -   ε′=real part of dielectric constant    -   ε″=imaginary part of dielectric constant    -   ν=frequency.

The lossy part of the dielectric constant (ε″) exhibits an extremelywide bandwidth in frequency, between 1 GHz to 500 GHz. Thus dielectricrelaxation is an intrinsically wide band phenomenon unlike Ohmic losses.What is not obvious is that values of the complex permittivity for wateruseable for absorptive duties can be realised if water is expanded orfoamed up thus diluting the water with an expansion agent andreducing-is its high complex permittivity. Expansion factors between 2and 200 kg/m³ accomplish this.

It is not possible to attain an aerosol of water droplets having thesedensities. It is possible to foam water up so that is exhibits suitableand efficient microwave absorptive characteristics between 2 and 120GHz.

Suitable foams may be commercially available shaving creams, carpetcleaners, fire fighting foams, garbage dump foam, or detergent foam, orany other suitable foam.

The density and thickness of the foam are extrinsic parameters that canbe controlled to suit specific frequencies. Inclusion or replacement ofthe water with other dipolar molecules furthermore allows an additionalmeans to modify and tune the electromagnetic properties of the foam forduty in other parts of the spectrum.

As the foam can be designed to have a bubble size much smaller than thewavelength of micro and millimeter wave radiation, the complexpermitivity in this limit can be shown to be easily modelled usingsimple mixing formulas such as:ε′_(foam)=1+(ε′_(m)−1)f  equation 1ε″_(foam)=ε″_(m) f  equation 2ε_(r) =ε′−ε″j  equation 3where the subscript ‘foam’ is the related quantity for the foamedmixture, the subscript ‘m’ is the related quantity for the prefoamedactive component held under pressure and ‘f’ is the volume fraction ofthe active component in the expanded medium, and ε_(r)=complexdielectric constant, ε″j=ε″√−1. It has been assumed in the aboveequation that the dielectric constant of the gas contained in the foamis 1. The above equation applies to specific frequencies up to a pointwhere this simple mixing formula is no longer applicable.

The prescription above described how efficient microwave characteristicscan be created by implementing a liquid based foam. Liquid based foamsalso exhibit other physical attributes that have not been obvious thatallow it alter the appearance of a treated object in other parts of theelectromagnetic spectrum.

The abovementioned foams are also excellent thermal insulators. Whileperforming a duty in the microwave and millimetre wave part of thespectrum, a hot body covered by the foam will appear to be at thetemperature of the foam as thermal infrared sensors will pick up thesurface temperature of the foam. Being a good thermal insulator, it willtake a prolonged period of time before heat from the coated surfacediffuses outwards towards the surface of the foam. Otherwise, liquidbased foams exhibit black body characteristics as most liquids exhibitemissivities close to 1.

The apparent thermal infrared temperature of the foam will be nearly itsactual temperature and thus the apparent temperature of any object maybe altered by treatment with a foam having the desired temperature. Anobjects apparent temperature may be controlled in the same way for dutyin the 3 to 5 micron mid infrared region.

This same water based foam can be used to suppress reflection of nearinfrared and visible electromagnetic waves if suitable dyes or pigmentsare incorporated into the prefoamed mixture.

In the visual part of the electromagnetic spectrum, the selectivereflection and absorption of radiation imparts colour. It has been shownthat if water soluble or water dispersible dyes and/or pigments areincorporated into the foam concentrate, the complex permittivity in themicrowave region is not substantially changed. The properties of the‘coloured’ foam in the optical region and near infrared take on thecharacter of the incorporated dye or pigment. Dyes active in the opticalregion can make the foam cloak have a camouflage appearance. These dyesor pigments can be bled into the feed stream in a controlled fashionduring deployment and in this way colour patterns can be built up.

In this way, a truly ‘DC to daylight’ (DC being zero frequency) can bedesigned from a surfactant stabilised aqueous foam. This material can becalled a “multispectral” foam as its properties are designed to controlreflection or the interaction of electromagnetic radiation over a widepart of the electromagnetic spectrum either through its permittivity orby way of other electromagnetic characteristics associated with thefoamed structure itself or its composition.

A foam material that simultaneously reduces reflection in the microwavethrough millimetre wave frequency band controls effective temperaturesin the 12 to 3 micron infrared and, by way of incorporated dyes orpigments, changes the colour of the foam so as to create a camouflagepattern not known previously.

It has been found that the surfactant and other additives do not degradethe desirable characteristics that would be exhibited by a pure form offoamed water. The main effect on the microwave properties is to decreasethe relaxation time of the water molecule due to an increase in theviscosity of the water (Journal of Chemical Physics, E. H. Grant, Volume26, page 1575, 1973). In fact, an increase in viscosity could be anadvantage in low frequency applications in that the relaxation time isincreased thus causing the loss factor to be higher at lowerfrequencies.

Typically, a surfactant stabilised foam would not only contain water asthe main constituent, but soluble polymers in addition to thesurfactant. These soluble polymers thicken the foam increasing itslongevity against drainage and its ability to stick well to anysubstrate. Such polymers could be polyacrylic acid, polyvinyl alcohol,guar gum and many others. Inorganic material like bentonite, athixotropic agent may also be used. A hydrophobic grade of fumed silicaas additive migrates to the surface as the foam dries out improving thecolour and surface texture of the foam thereby altering the surfacestructure and colour and thus compensating for colour changes occurringwhen the material dries out.

The soluble polymer or surfactant additives may influence the microwaveproperties of the foam in two ways. Firstly, it increases the viscosityof the aqueous phase thus reducing the relaxation frequency and,secondly, it can increase or decrease the permittivity of the foamdepending upon its intrinsic permittivity.

A “water-based multispectral foam” is one which may contain water as theprincipal component and in addition, substances falling into a generalclass of chemicals as listed below:

-   -   1) surfactants, both ionic and non-ionic;    -   2) soluble polymers or in situ crosslinkable monomers of any        molecular weight;    -   3) a base to neutralise or partially neutralise the ionic        surfactant;    -   4) soluble dyes or water dispersible pigments or dyes;    -   5) other pure substances which are soluble in the liquid base        that either improve or otherwise alter the overall permittivity        of the mixture, e.g. by way of viscosity modification;    -   6) a gas which could be air, light hydrocarbon liquids such as        butane or any other gas or liquid which either acts as the        blowing agent and/or propels the mixture out of a container;    -   7) all of the above contained at the right temperature dispersed        as a foam.

DESCRIPTION OF EXAMPLES

The invention will now be described by way of examples as set out below.

In FIG. 2 is shown the permittivity of a conventional shaving cream inthe 11 to 17 GHz band. The density for this freshly foamed material isabout 70 kg/m³. This shaving cream has about a 12 weight % solidscontent and thus is about 88% water. Thus this foam consists ofapproximately 93% expansion agent.

Based on simple effective medium theory calculations using data for purewater taken from the Hasted reference, it is possible to predict thecomplex permittivity for a water/air mixture containing 93 volume % air.

At a single frequency of 12.82 GHz for example, predictions give thevalue for the real part of the permittivity to be 3.1 and the imaginarypart to be 2.42. Comparing this with the measured values of the foammaterial at the same frequency (2.48-0,65j) yields an over estimationfor the teal part and an over estimation for the imaginary part. It isfelt that the difference is due to the viscosity related change inrelaxation frequency which has shifted the complex part of thedielectric constant to lower values. The soluble polymer is alsoresponsible for increasing the dielectric constant to higher values,however, the surfactant and any polymeric additives are at relativelysmall quantities to effect the dielectric constants directly.

Another way to compare these measurements with what has been measuredfor pure water is to consider the ratio of the imaginary part of thedielectric constant to the real part, i.e., tan (delta), being ε″/ε′.For pure water at 12.82 GHz, tan(delta) is 1.1.

In FIG. 3 is shown the permittivity of the same foam containing 1 volume% water soluble ink solution. Tan (delta) for this material was measuredto be 0.45. This is an increase in tan (delta) from the foam without inkof 0.33. This increase may not be entirely due to the ink itself butalso to the admixture of the solvent the ink solution contains.

FIG. 4 shows the permittivity measured data on the foam where 20 weight% methanol has been added. Tan (delta) in this case is 0.8, a dramaticincrease over that of nascent foam. Methanol has a relaxation frequencyin its pure state at about 3.5 GHz. Together with the water basedcomponent, the magnitude of the complex part of the permittivity has nowincreased tan (delta).

The data above was measured on a conventional cosmetic product, namelyshaving cream. This product consists of an unknown composition andbecause it is canned only for the purpose for which it was intended, onecannot change the formulation to suit specific requirements. Because theshaving cream was designed for human skin contact, it contains a numberof additives that may not be necessary for the practicing of this art.

The next series of experiments that are reported below use a general andhome-made formula that is canned with different additives and gas loads.The concentrate consists of:

1) water: 85.31 weight % 2) non-ionic surfactant: 7.31 weight % 3) ionicsurfactant: 2.04 weight % 4) humectant: 2.03 weight % 5) base to pH 6.5:0.223 weight % 6) long chain alcohol: 3.07 weight % 7) Butane/propane(30:70) mixture variable weight % on total liquid.

The concentrate contains approximately 15 weight percent solids.

FIG. 5 (sample 1) below shows the permittivity (measured in a coaxialsample holder) of a 98 gram load of the concentrate loaded with 2 gramsof liquid butane/propane (vapour pressure 40 kilo pascal).

FIG. 6 (sample 2) is the same foam concentrate as in sample 1 loadedwith 3 grams of liquid butane/propane (vapour pressure 40 kilo pascal).

FIG. 7 (sample 5) is the same foam concentrate as in sample 1 loadedwith 6 grams of liquid butane/propane (vapour pressure 40 kilo pascal).

FIG. 8 (sample 6) is the same foam concentrate as in sample 1 loadedwith 7 grams of butane/propane (vapour pressure 40 kilo pascal).

The data shown in FIGS. 5 through 8 demonstrates how the permittivity ofthe foam can be controlled through the amount of liquid butane used asthe blowing agent and expulsion medium. This determines the ultimatedensity of the foam.

To further demonstrate the flexibility in the above formula, it has beenshown that the water in the above formula can be replaced by sea waterwithout effecting optimal properties.

It is not enough to make a foam having desirable permittivites. The samefoam must also be mechanically stable and have longevity, retaining itswater content and cellular structure for long periods of time.

Table 1 summarizes typical densities achieved.

TABLE 1 Grams of foam concentrate grams butane 40 foam density (kg/m³)98 2 126 98 3 112 96 4 77 97 5 54 96 6 49 97 7 37

Although a wide range of densities can be obtained by control of theexpansion agent concentration, those reported in Table 1 are perhaps themost valuable.

Other substances can be added to the foam concentrate in an effort topigment the foam so that it can also operate as an absorber of nearinfrared and visible electromagnetic waves. The Figures show how theseadditives effect the microwave permittivity.

In FIG. 9 (sample 7) is shown the permittivity of a sample consisting of100 grams of foam concentrate and 0.71 grams of ‘multi-dispersal carbonblack’. This pigment is a dispersion of carbon black in water andethylene glycol having a 42 weight % solids content. The carbon blackwas milled down to below 5 microns. 97 grams of the multi-dispersalblack/foam concentrate was canned with 5 grams of butane/propane (vapourpressure 40 kilo pascal). The resultant density was 54 kg/m³.

FIG. 10 (sample 8) shows the permittivity of a sample consisting of 100grams of the foam concentrate and 1.77 grams of the multi-dispersalblack pigment. 100 grams of this mixture was canned with 5 grams ofbutane/propane (vapour pressure 40 kilo pascal). The resultant densitywas 52 kg/m³.

FIG. 11 (sample 9) shows the permittivity and permeability of a sampleconsisting of 100 grams of foam concentrate mixed with 8.89 grams of‘multi-dispersal iron oxide black’ produced by the same company. Theiron oxide (magnetite) was milled down to below 0.5 microns anddispersed in water/ethylene glycol solution to 60 weight %. 100 grams ofthis pigment/foam concentrate was canned with 5 grams of butane/propane(vapour pressure 40 kilo pascal). The resultant density was 62.7 kg/m³.

To further demonstrate the wide variety of properties accessible byliquid based foams, one can prescribe a ‘winter formula’ for use totemperatures as low as −15 degrees C.

1) water: 54.39 weight % 2) non-ionic surfactant: 6.83 weight % 3) ionicsurfactant: 1.91 weight % 4) humectant: 1.89 weight % 5) base to pH 6.5:0.208 weight % 6) long chain alcohol: 2.87 weight % 7) antifreeze: 31.88weight % 8) propane 5 weight % on total liquid

Another formulation with superior properties below 5 GHz, and one thatalso is applicable to sub-zero temperatures is:

1) antifreeze: 87.31 weight % 2) non-ionic surfactant: 7.31 weight % 3)ionic surfactant: 2.04 weight % 4) base to pH 6.5: 0.223 weight % 5)long chain alcohol: 3.07 weight % 6) propane 5 weight % on total liquid

This example demonstrates that the foam need not contain water at all.

The reflectivity loss that can be achieved if a flat metal plate iscovered with a 30 mm thick even layer of water based foam is explainedbelow. The two samples were measured in a free space facility at between11 and 17 GHz.

In FIG. 12 is shown the reflectivity loss down from a metal plate forthe shaving cream at 30 mm thick. This material has a density of 70kg/m³.

In FIG. 13 below is shown the reflectivity loss down from a metal platefor a sample of fire fighting foam. The foam was air blown and had adensity of 50 kg/m³.

It is shown the reflectivity loss that can be achieved if a flat metalplate or a corner reflector is covered or filled respectively, withwater based foam. The samples were measured in the free space facilityat 94 GHz. The experiment was multipurpose in that the effect of waterspray and dust were measured. The order of the event chronology isdescribed in the figure captions.

In FIG. 14 is shown the reflectivity loss down from a 10 m² cornerreflector treated with foam and also tested with dust and water spray.This material has a density of 61 kg/m³.

The references in the graph in FIG. 14 indicate the following:

Event Chronology Reflectivity relative References: to base  1: clean 10m² corner reflector (base)    0 dB  2: reflector completely filled withfoam −36 dB  3: heavy layer of dust applied to surface −38 dB of foam 4: first water spray −33 dB  5: second water spray −34 dB  6: thirdwater spray −36 dB  7: foam partially removed from reflector −33 dB  8:more material removed from reflector −32 dB  9: a thin layer of foamleft on reflector −17 dB surfaces 10: a thin layer of foam left on asingle  −9 dB surface 11: reflector washed clean but still wet  −1 dB

In FIG. 15 is shown the reflectivity loss down from a polished metalplate treated with foam in various ways. The foam density was 30 kg/m³.

The references in the graph in FIG. 15 indicate the following:

Event Chronology reflectivity relative References: to base 1: platecovered with 20 mm of foam −30 dB 2: plate oscillating in wind n/a 3:foam sliding off plate exposing metal −20 to −18 dB 4: foam repaired −30dB 5: water spray applied −30 to −38 dB 6: foam sliding off plateexposing metal −38 to −22 dB 7: clean plate (base)    0 dB

In FIG. 16 is shown the total reflectivity loss in the UV (Ultraviolet)through to the near IR (Infrared) range of frequencies of a sample dyedwith carbon black at 2.34 weight %.

The above examples indicate that a degree of control exists in designingsurfactant stabilised foams to perform the role of a microwave absorberor as an electromagnetic energy adaptation material. The controlparameters such as the expansion factor, amount of surfactant, and theaddition of dyes and other small dipolar molecule liquids allow this newmaterial to be engineered to suit a wide variety of absorptioncharacteristics at different frequencies.

In addressing the mechanical integrity issue, it has been demonstratedthat foam concentrate mixtures containing soluble polymers provide for afoam stable for over 12 hours without degradation of the effectivepermittivity, this depending upon the ambient temperature and humidity.In a more advanced formulation, it has been demonstrated that apolyvinyl alcohol based foam concentrate can be blown simultaneously, asa binary charge with a sodium borate solution.

The borate crosslinks the polyvinyl alcohol almost instantly creating astiff expanded foam with excellent mechanical strength and longevity.

In another formulation, it has been demonstrated that a polyacrylic acidbased foam concentrate can be neutralised with ammonium hydroxide up toa critical point where the concentrate is on the verge of gelling.

After blowing the foam, the excess ammonia is free to evaporate into thebutane gas filled cells of the foam or out of the foam altogether. Thedepletion of ammonia from the liquid phase precipitates the acrylic acidpolymer producing a stiff expanded gel of exceptional mechanicalintegrity.

In use, for instance to camouflage an object for military purposes theelectromagnetic energy adaptation material is foam-sprayed onto theobject, or, in a zone distant from the object, so as to minimise oralter detection of such an object.

In the case of radar detection, the density and the composition of thematerial, affecting the permittivity, must be controlled so as toachieve lower reflection in the case of a metallic object, or in thecase of a cave the cavities are filled up with foamed material resultingin the permittivity of the rock or sand structure.

In the case of thermal detection the temperature of the foamed materialmust be controlled to have an ambient temperature, or in the case ofacting as a decoy, then its temperature should be controlled to behigher than ambient.

In the case of visual detection, the foamed material is pigmentated soas to cause appropriate blending with the surroundings.

1. A method of minimizing or altering detection, for military purposes by electromagnetic detection apparatus, of an object by means of an electromagnetic energy adaptation material, said method comprising at least one of the steps selected from the group consisting of: (a) coating an object at least partially by means of an electromagnetic energy adaptation material; and (b) coating a zone spaced away from such an object at least partially by means of an electromagnetic adaptation material; said electromagnetic adaptation material comprises a water-based foam constituted by a liquid-based mixture of at least one dipolar molecular liquid with at least one ionic surfactant and constituting a base agent adapted to at least partially neutralize the ionic surfactant; said mixture adapted to being held in a container under a pressure higher than atmospheric pressure by an alkane emulsifiable gas and adapted to expand to form the water-based foam after being released from the container as a result of lower atmospheric pressure than the pressure in the container; said alkane emulsifiable gas including at least one compound selected from the group comprising short-chained alkanes, ethane, butane, propane and mixtures thereof; said water-based foam having a density of 30-126 kilograms per cubic meter; said density of the water-based foam being determined by the amount of emulsifiable gas used to pressurize the mixture in the container; said density determining the microwave and thermodynamic properties of the material; said material having at least one characteristic selected from the group of characteristics consisting of being adapted to absorb electromagnetic energy, being adapted to alter the reflections of electromagnetic energy, and being adapted to emit electromagnetic energy; said characteristic being a result of Debye relaxation and blackbody emissivity characteristics of the dipolar molecular liquid and a result of the intrinsic thermal conductivity of the water-based foam based on the density of the water based foam; said dipolar molecular liquid being at least one compound selected from the group consisting of water, an alcohol, glycol and methanol; and said electromagnetic energy detection apparatus being at least one selected from the group consisting of radar equipment, thermal detection apparatus and laser detection equipment.
 2. The method as claimed in claim 1, further comprising providing at least one component selected from the group consisting of soluble dyes, water dispersible dyes, water dispersible pigments and viscosity modifiers to the mixture.
 3. The method of claim 1, wherein the alkane emulsifiable gas constitutes 2 to 6.7 weight % of the mixture.
 4. The method of claim 1, wherein: (a) coating an object comprises coating a continuous surface of an exposed material of the object to mask detection of the object by an electromagnetic detection apparatus; and (b) coating a zone spaced from the object comprises forming a coating which masks detection of the object by an electromagnetic detection apparatus. 